IFF_PREFERRED
{ "preferred", IFF_PREFERRED, setifflags, 0, AF_INET6 },
{ "-preferred", -IFF_PREFERRED, setifflags, 0, AF_INET6 },
{ IFF_PREFERRED, AF_UNSPEC, "preferred" },
{ IFF_PREFERRED, "PREFERRED" },
{ IFF_PREFERRED, 0, "PREFERRED" },
#define IPIF_PREFERRED IFF_PREFERRED /* Prefer as source address */
IFF_PREFERRED|IFF_TEMPORARY|IFF_DUPLICATE)